Chromatin

How to pack 2 meters of DNA into a nucleus of .006 mm?

  1. nucleosomes (11 nm fiber)
    • nuclease digestion of chromatin releases 11 nm particles with 150 bp of DNA
    • histone proteins (H1, H2A, H2B, H3, and H4)
    • DNA is wrapped around a histone core of 2 ea. of H2A, H2B, H3, H4
    • this gives an 11 nm fiber and a 6-fold packing
  2. solenoid
    • H1 pulls the nucleosomes together and they coil into a solenoid
    • one H1/nucleosome
    • 25 - 30 nm thick and a 6&endash;7-fold packing
  3. folded loops (300 nm fiber)
    • loops are attached to a scaffold
    • topoisomerase II (at the scaffold attachment site) supercoils the DNA
    • 4.5 - 112 kb long
    • transcriptionally active DNA is in the loops
  4. radial loops
    • coil the scaffold

[ Biol 207 ] [ Bell ] [ CSU Chico ] [ Library ]
This document is maintained by: Jeff Bell
Last Update: Wednesday, August 12, 1998